JP6275038B2 - Recovery of carboxylic acids from their magnesium salts by precipitation with hydrochloric acid, useful for fermentation broth treatment - Google Patents

Description

The present invention is from the group consisting of 2,5-furandicarboxylic acid, fumaric acid, adipic acid, itaconic acid, citric acid, glutaric acid, maleic acid, malonic acid, oxalic acid, and fatty acids having more than 10 carbon atoms. It is directed to a process for preparing selected carboxylic acids.

The production of the carboxylic acid results in various undesirable by-products, especially when produced by fermentation. The fermentation process where the carboxylic acid is excreted by the microorganism results in a decrease in pH. It is a common practice to add a base to the fermentation medium in order to neutralize the pH, since such a decrease in pH can impair the metabolic processes of the microorganism. As a result, the carboxylic acid produced in the fermentation medium is typically present in the form of a carboxylate salt.

The disadvantage of obtaining the carboxylic acid in the form of a carboxylic acid salt from the fermentation process is that one or more to separate the carboxylic acid from the salt, ie to convert the salt to a carboxylic acid. Additional steps are typically required, which results in loss of carboxylic acid and / or carboxylate salt, ie, a reduction in overall fermentation or process yield.

A further disadvantage of such processes is that they typically result in considerable salt waste. For example, the separation step often involves acidification of the carboxylate with sulfuric acid, resulting in sulfate as waste.

The object of the present invention is to provide a separation step in which the carboxylic acid is separated from the salt solution with a suitable conversion yield.

It is a further object of the present invention to provide a process that is free or substantially free of salt waste.

At least one of these purposes is 2,5-furandicarboxylic acid, fumaric acid, adipic acid, itaconic acid, citric acid, glutaric acid, maleic acid, malonic acid, oxalic acid, and fatty acids having more than 10 carbon atoms A process for preparing a carboxylic acid selected from the group of
Magnesium carboxylate selected from the group of 2,5-furandicarboxylic acid, fumaric acid, adipic acid, itaconic acid, citric acid, glutaric acid, maleic acid, malonic acid, oxalic acid, and fatty acids having more than 10 carbon atoms Preparing the process,
Acidifying the magnesium carboxylate with hydrogen chloride (HCl), thereby obtaining a solution containing carboxylic acid and magnesium chloride (MgCl ₂ );
Optionally, a thickening step, wherein the solution comprising carboxylic acid and MgCl ₂ is thickened.
It was satisfied by providing said method comprising the step of precipitating the carboxylic acid from the solution containing the carboxylic acid and MgCl ₂ , thereby obtaining a carboxylic acid precipitate and a MgCl ₂ solution.

The fermentation process can also result in impurity profiles that are difficult to process in further downstream purification steps. The fermentation process depends in principle on the carboxylic acid to be produced and can thus produce different impurity profiles (for example not only at the concentration level, but also at the type of impurities that are potentially present). That is, downstream processing steps for further thickening and purification can also vary with the carboxylic acid. In particular for the mentioned carboxylic acids of the invention, the process of the invention starts not only with magnesium carboxylates that can be made by chemical synthetic processing routes, but also magnesium carboxylates that can be made by fermentation, if applicable. It has been found that this is an efficient and complete method for the production of these carboxylic acids used as materials.

We have found that the addition of HCl to the magnesium salt of the selected carboxylic acid and subsequent precipitation of the carboxylic acid from the solution is a very efficient separation of the carboxylic acid from the magnesium carboxylate solution. Found to bring.

In particular, it has been discovered that the selected carboxylic acid is precipitated with very high efficiency from a carboxylate solution acidified with HCl. Without wishing to be driven by any theory, we predict that the high efficiency of the precipitation is due to the particularly high salting out effect of MgCl _{2 in} the solution. In particular, the salting out effect is expected to be caused by a specific combination of HCl, magnesium and the selected carboxylic acid of the present invention. Since the salting out effect is generally difficult to predict, the particular high salting out effect for these acids observed in the process of the present invention was surprising to the inventors.

That is, when using the method of the present invention for the carboxylic acids specifically mentioned above, a carboxylic acid precipitate can be obtained in high yield from a magnesium carboxylate solution, which can be obtained, for example, in a fermentation process. Fermentation mixture. Furthermore, the resulting carboxylic acid precipitate has a relatively high purity. This is because the precipitation step in the method of the present invention does not result in a large amount of precipitation of compounds other than carboxylic acids. Furthermore, a magnesium chloride solution is obtained. This solution can be further processed as described below.

In addition, certain choices for HCl and magnesium carboxylate provide salt waste reduction, especially when combined with a pyrolysis step.

Preferably, the method further comprises the following steps:
Subjecting the MgCl ₂ solution to a pyrolysis step at a temperature of at least 300 ° C., thereby decomposing the MgCl ₂ into magnesium oxide (MgO) and HCl; and
Optionally dissolving the HCl formed in the pyrolysis step in water, thereby obtaining an HCl solution; and optionally contacting the MgO with water, thereby obtaining Mg (OH) ₂ . The Mg (OH) ₂ is optionally recycled for use in a fermentation process, preferably the fermentation process provided with the magnesium carboxylate from the first step.

The advantage of these additional steps is that a process can be obtained which has no or substantially no salt waste. The HCl solution can be reused in the acidification step of the process of the present invention. The Mg (OH) ₂ can be reused for use in the fermentation process.

The term “carboxylate” as used herein refers to the conjugate base of a carboxylic acid, which can generally be represented by the formula RCOO ⁻ . The term “magnesium carboxylate” refers to the magnesium salt of the carboxylic acid to be prepared in the process of the present invention.

The term “carboxylic acid corresponding to the carboxylate” refers to a carboxylic acid obtained by acidifying the carboxylate. It can therefore also be referred to as an acidified carboxylate. The carboxylic acid corresponding to the carboxylate can generally be represented by the formula RCOOH.

The term “precipitate” as used herein refers to the formation of a solid starting from a fully dissolved state. Carboxylic acids can be precipitated in crystalline or amorphous form. The carboxylic acid can also be purified by precipitating the carboxylic acid according to the method of the present invention. When the magnesium carboxylate solution contains dissolved impurities, precipitation of the carboxylic acid typically separates the carboxylic acid from such impurities.

The term “solution to be precipitated” as used herein refers to a solution that is to be subjected to precipitation. Typically, the term refers to a solution containing carboxylic acid and MgCl ₂ obtained after acidification, optionally subjected to a thickening step and / or a step where extra MgCl ₂ is added. And a solution containing carboxylic acid and MgCl ₂ obtained after. However, in the case of a second or further precipitation step, the term “solution to be precipitated” refers to the MgCl ₂ solution obtained after the last or most recent precipitation step, optionally this solution is the concentration step and / or Or it refers to the MgCl ₂ solution obtained after being subjected to the step of adding excess MgCl ₂ . Such MgCl ₂ solution may still contain carboxylic acid, which can be obtained by subjecting it to a second or further precipitation step.

The method of the present invention comprises 2,5-furandicarboxylic acid, fumaric acid, adipic acid, itaconic acid, citric acid, glutaric acid, maleic acid, malonic acid, oxalic acid, and a group of fatty acids having more than 10 carbon atoms. Has been found to work efficiently for carboxylic acids selected from: Thus, the magnesium carboxylate can be selected from magnesium salts of these carboxylic acids. Good results have been obtained with a carboxylic acid selected from the group consisting of adipic acid, itaconic acid, 2,5-furandicarboxylic acid, and fumaric acid.

The magnesium carboxylate provided in the method of the present invention can be obtained in a fermentation process.

The magnesium carboxylate can be provided in a solid (eg, crystalline form). Alternatively, the magnesium carboxylate can be in dissolved form, for example as part of a solution or suspension. Such a solution or suspension containing dissolved magnesium carboxylate may be aqueous and may be obtained in particular in a fermentation process. An example of a suspension can be, for example, a suspension containing dissolved magnesium carboxylate and insoluble biomass, such as a fermentation broth. When the magnesium carboxylate is prepared in dissolved form, the magnesium carboxylate solution or suspension is 1 to 700 g, preferably 100 to 600 g, more preferably 200, per liter of solution or suspension. May have a concentration of ˜500 g magnesium carboxylate.

When the carboxylate is provided as a solution or suspension, the magnesium carboxylate concentration at which carboxylic acid precipitation occurs upon acidification can depend on the HCl concentration. For example, when the carboxylate is acidified using an HCl solution having a high HCl concentration (eg, 20-30% by weight), precipitation of the carboxylic acid may occur at a relatively low carboxylate concentration (eg, 1-10% by weight or Can occur around 1-10% by weight). However, when using lower HCl concentrations (eg 10-20% by weight), higher carboxylate concentrations (eg 10-50% by weight) may be required for precipitation to occur. For practical reasons, the upper limit of magnesium carboxylate concentration in the magnesium carboxylate solution is the maximum solubility of magnesium carboxylate at a maximum temperature of 75 ° C. This concentration is typically about 20 wt% magnesium carboxylate or lower, based on the total weight of the solution. However, it can vary for the particular carboxylate used. A concentration higher than 20% by weight may require the solution to have a temperature of 75 ° C. or higher in order to bring the magnesium carboxylate into fully dissolved form. This temperature is bad for the device with respect to the corrosion sensitivity of the materials used in the presence of HCl.

In order to obtain as much carboxylic acid as possible after acidification and precipitation, the carboxylate concentration proceeding to the acidification is preferably as high as possible. When the magnesium carboxylate is provided as a solution, the upper limit of magnesium carboxylate concentration is determined by the solubility of the magnesium carboxylate and the temperature at which the device is still sufficiently resistant to corrosion due to HCl. When the carboxylate is provided as a suspension, typically the agitation of the suspension determines the upper limit. When the carboxylate is prepared as a solid cake, the solid-liquid separation and the resulting attached water typically determines the upper limit. In order to support high carboxylic acid yields after acidification and precipitation, the HCl concentration is preferably as high as is economically feasible. This is because the introduction of excess water dilutes the system. A combination of the above mentioned input concentrations of carboxylate and HCl should desirably result in a situation where MgCl ₂ remains in solution and as much carboxylic acid as possible is precipitated during the precipitation step. . One skilled in the art can vary the two concentrations to obtain the desired result. For example, good results have been obtained with a combination of 15-25 wt% HCl and 20-50 wt% magnesium carboxylate concentrations at 40-75 ° C.

If the magnesium carboxylate solution or suspension is obtained from a fermentation process that does not have a sufficiently high magnesium carboxylate concentration, the solution may be concentrated, for example by evaporation.

In a preferred embodiment of the present invention, magnesium carboxylate is produced directly to make processing as simple as possible, as opposed to first performing fermentation and then adding a base to form magnesium carboxylate. And in order to prevent the use of additional processing steps, the magnesium carboxylate is obtained in a fermentation using a magnesium-based base for neutralization. The method of the present invention further preferably comprises a magnesium carboxylate fermentation at 25-60 ° C., wherein the carboxylate solution obtained when adding the base in the fermentation contains 1-30% by weight of magnesium carboxylate. As a result, the magnesium carboxylate as a fermentation product does not precipitate directly. Direct precipitation of magnesium carboxylate in the fermentation broth during fermentation requires fairly extreme fermentation conditions, such as magnesium carboxylate concentrations above 40% or even above 50% by weight, which Unfavorable for the microorganism, fermentation yield and / or equipment. In order to precipitate magnesium carboxylate from the fermentation broth after fermentation, preferably another precipitation step is applied. Such a precipitation step is, for example, a thickening step as described above or a cooling precipitation as further described below. The precipitate thus obtained can then be dissolved in water to form an aqueous magnesium carboxylate solution or suspension.

The method of the present invention further includes an acidification step in which the magnesium carboxylate is acidified with HCl, thereby obtaining a solution containing the carboxylic acid and MgCl ₂ . The inventors have discovered that HCl is preferred as an acidifying agent over other acids such as H ₂ SO ₄ . First, the use of HCl provides efficient precipitation, such as the advantageous salting out effect described above. In particular, the presence of MgCl ₂ reduces the solubility of the carboxylic acid, which results in a more efficient precipitation of the acid. Furthermore, the reaction of magnesium carboxylate with HCl results in a salt (MgCl ₂ ) having a relatively high solubility, especially compared to other magnesium salts containing MgSO ₄ and also to many carboxylic acids. . High solubility of the salt obtained by acidification is desirable because as little salt as possible should be precipitated in the precipitation step. Therefore, the maximum concentration of carboxylic acid in the solution to be precipitated is determined in part by the solubility of the salt obtained in the acidification step. That is, if the salt has high solubility, a high carboxylic acid concentration can be obtained without precipitation of the salt, which results in efficient precipitation of the carboxylic acid.

Acidification is typically performed using excess HCl. The excess is preferably small, so that the MgCl ₂ solution obtained after precipitation is not highly acidic, which may be undesirable in view of further processing of such a solution. For example, the excess of HCl used can be such that the resulting MgCl ₂ solution after precipitation has a pH of 1 or higher, such as a pH of about 1.5. The person skilled in the art knows how to calculate the maximum allowable excess for such one or higher pH based on the reaction stoichiometry. In order to obtain a sufficiently complete acidification, MgCl ₂ solution is該得is preferably lower than 4, more preferably a pH lower than 3.

HCl acidification is, for example, by contacting the magnesium carboxylate with HCl, for example by contacting the magnesium carboxylate (in solid, suspension or solution) with an HCl aqueous solution or with a magnesium carboxylate solution or suspension. This can be done by contacting the turbid material with HCl gas.

If an HCl solution is used in the acidification step, preferably it comprises at least 5 wt% HCl, more preferably at least 10 wt%, even more preferably at least 20 wt% HCl. Such a concentration is generally sufficient to acidify the magnesium carboxylate. High HCl concentrations are desirable because of the salting out effect mentioned above. Due to the low boiling point of HCl and the HCl / H ₂ O azeotrope, the HCl concentration in the HCl solution will typically not be higher than 40%, especially when the HCl solution is used at atmospheric pressure. Preferably, the HCl concentration is used at a HCl concentration of 15 to 25% by weight, based on the total weight of the HCl solution. Nevertheless, HCl concentrations of up to 100% may also be used, in which case the HCl solution typically has an increased pressure (eg higher than atmospheric pressure) and optionally a lower temperature (eg higher than 20 ° C.). Low).

If HCl gas is used, the HCl gas can be contacted by contacting it with a carboxylate solution or suspension. In particular, HCl gas can be blown through the solution or suspension. If HCl gas is used, HCl can be obtained from a pyrolysis step, such as that described further below.

Preferably, the acidification is performed at a temperature of 75 ° C. or lower. At higher temperatures, it becomes uneconomical to adapt the device to its harsh conditions. In view of the freezing point of water, acidification is typically performed at temperatures above 0 ° C. A temperature higher than 20 ° C is preferred to avoid the use of a cooling machine. Temperatures of 40 ° C. or higher, or even 60 ° C. or higher are even more preferred because more magnesium carboxylate can be dissolved at these higher temperatures. The temperature of the magnesium carboxylate solution or suspension is typically determined by and corresponds to the temperature at which the acidification takes place.

The method of the invention may comprise a thickening step, in which the solution obtained after acidification with HCl is thickened. Higher concentrations of carboxylic acid in the solution will increase the efficiency of carboxylic acid precipitation. The thickening step can be performed by evaporation. In the thickening step, 10 to 90% of the total amount of water present in the solution can be removed. However, preferably MgCl ₂ is not precipitated as a result of the enrichment. Therefore, the solution obtained after acidification is preferably thickened lower MgCl ₂ concentration than or equal the saturation point and the saturation point of MgCl _2.

The method of the invention further comprises precipitating the carboxylic acid from the solution obtained in the acidification step or from the solution obtained in the concentration step, if present. This step can be referred to as the (first) precipitation step. Precipitation may be achieved by any precipitation method known in the art, such as reactive precipitation, or by cooling, concentrating and evaporating the solution to be precipitated, or the solution to be precipitated. This can be done by adding an antisolvent to the solution.

Precipitation is preferably established by acidifying the magnesium carboxylate with HCl. This type of precipitation can be referred to as reactive precipitation. In reactive precipitation, precipitation occurs during acidification. As a result, acidifying the magnesium carboxylate and precipitating the carboxylic acid thus obtained are carried out as one step. Accordingly, the method of the present invention comprises (as described above) optionally providing a magnesium carboxylate obtained in a fermentation process; and acidifying the magnesium carboxylate with HCl (eg, HCl aqueous solution) This would include obtaining a carboxylic acid precipitate and a MgCl ₂ solution. It is noted that the precipitation step actually results in a suspension with the carboxylic acid precipitate present in the MgCl ₂ solution.

Reactive precipitation can be performed by selecting conditions in the acidification step such that immediate precipitation of the carboxylic acid can occur. Those skilled in the art know how to establish such conditions. In particular, the magnesium carboxylate concentration can be selected such that acidification with HCl results in a carboxylic acid concentration that is higher than the saturation point of the carboxylic acid. As those skilled in the art will know, the value for the saturation point depends on the carboxylic acid used.

The precipitation step can also be carried out by cooling the solution to be precipitated, for example the solution formed in the acidification step or, if present, the solution obtained in the concentration step. This type of precipitation can be referred to as cold precipitation. The cooling step may require that the solution to be precipitated is first heated to a temperature at which substantially all MgCl ₂ and carboxylic acid are dissolved. The solution to be precipitated can be cooled from a temperature above the nucleation temperature of the carboxylic acid in the solution to a temperature below the nucleation temperature of the carboxylic acid in the solution. The nucleation temperature is the highest temperature at which solids, especially precipitates, are formed. This temperature depends inter alia on the concentration of MgCl ₂ , the presence of carboxylic acids and other components. It is therefore not possible to give a single temperature value for the nucleation temperature. In general, however, the solution to be precipitated is cooled from a temperature of at least 35 ° C. to a temperature of less than 30 ° C., preferably to a temperature of at least 40 ° C. to less than 25 ° C. A larger temperature difference makes it possible to increase the yield of the carboxylic acid precipitate. In the case of cold precipitation, the carboxylic acid concentration before cooling is preferably as close to the solubility as is economically feasible. The carboxylic acid concentration may be equal to the saturation point of the carboxylic acid, or may be at most 5 g / L lower than the saturation point of the carboxylic acid, preferably lower than 10 g / L.

Furthermore, precipitation can be established by concentrating the solution containing the carboxylic acid and MgCl ₂ , preferably by evaporation. Evaporation of a portion of the solvent of the solution containing the carboxylic acid and MgCl ₂ results in a higher concentration of the carboxylic acid and a stronger salting out effect, which increases precipitation.

Furthermore, precipitation can be established by adding an antisolvent to the solution to be precipitated. Examples of antisolvents are alcohols, ethers and ketones.

Preferably, the MgCl ₂ solution obtained after precipitation may be subjected to a second and / or further precipitation step, thereby forming an additional carboxylic acid precipitate and a second and / or further MgCl ₂ solution. To do. The second or further precipitation step is performed to recover at least a portion of the carboxylic acid remaining in the MgCl ₂ solution obtained in the previous precipitation step. In this case, the previous precipitation step of the present invention may be referred to as the first precipitation step. The MgCl ₂ solution obtained in the first precipitation of the process may still contain a small amount of carboxylic acid. A second precipitation step can be performed to recover at least a portion of the carboxylic acid. Such a second precipitation step may be performed under the same conditions as the first precipitation step, and may include a thickening step and / or the addition of MgCl ₂ performed prior to the precipitation step.

In a preferred embodiment, the method of the invention comprises a first precipitation reaction, which is a reactive precipitation step, after which the MgCl ₂ solution obtained in this step is subjected to a cooling and / or evaporation step. Is done. The cooling and / or evaporation step is a further precipitation step in which additional carboxylic acid is precipitated and the loss of carboxylic acid and the process yield are thus improved.

Prior to any precipitation step, magnesium chloride can be added to the solution to be precipitated or to the HCl solution. This solution to be precipitated can be a solution containing the magnesium carboxylate solution (for example in the case of reaction precipitation) or a solution containing carboxylic acid and magnesium chloride (as obtained in the acidification step). Such added magnesium chloride can increase the salting out effect and thereby increase precipitation of the carboxylic acid.

Preferably, the method further comprises
Subjecting the MgCl ₂ solution to a pyrolysis step at a temperature of at least 300 ° C., thereby decomposing the MgCl ₂ into MgO and HCl; and dissolving the HCl formed in the pyrolysis step in water. And thereby obtaining an HCl solution; and contacting the MgO with water, thereby obtaining Mg (OH) ₂ .

As described above, the advantage of these additional steps is that a process can be obtained that has no or substantially no salt waste.

Pyrolysis as described herein can also be suitably applied in the method of the present invention. Thus, the pyrolysis used in the present invention can be performed by spraying a MgCl ₂ solution and contacting it with a hot gas stream. The temperature of the hot gas is equal to the temperature at which pyrolysis takes place, as described below.

The combination of pyrolysis in acid / salt separation of magnesium carboxylate from the fermentation process has not been previously described to the best of Applicants' knowledge. We have found that MgCl ₂ can be pyrolyzed by pyrohydrolysis at relatively low temperatures (eg, in contrast to CaCl ₂ which begins to decompose at temperatures of about 800 ° C. or higher). understood. This is advantageous because the formed MgO is still highly reactive and can be used effectively, for example, in fermentation.

Equipment suitable for performing pyrolysis is known in the art. Pyrolysis can be performed using a roaster, such as a spray roaster or fluidized bed roaster. Such a device can be obtained, for example, with SMS Siemag. The use of a spray roaster is preferred. Spray roasters have low energy costs (as compared to fluid bed roasters) because they require relatively low temperatures (as described below). Spray roasters have also been found to produce reactive MgO particles, which are very suitable for use as neutralizing agents in fermentation.

Preferably, the pyrolysis is performed at a temperature of at least 300 ° C., which is the lowest temperature at which MgCl ₂ decomposes. Preferably, the pyrolysis is performed at a temperature of at least 350 ° C, such as 350-450 ° C. Due to energy costs, the temperature is preferably below 1000 ° C, more preferably below 800 ° C. For example, the temperature at which pyrolysis is performed can be 350-600 ° C or 300-400 ° C. In addition, it is not desirable to use a temperature that is too high for the pyrolysis step, as it reduces the reactivity of the formed MgO, so that it is more for use as a neutralizing agent in fermentation. It is not suitable.

Pyrolysis as applied in the present invention is preferably performed at a pressure of 0.1 to 10 bar. However, the use of elevated pressure is undesirable because of the increased risk of corrosion by the HCl that cannot be condensed. Preferably, especially when using a roaster, the pyrolysis is carried out at atmospheric pressure in order to avoid unnecessary energy costs and the need for expensive high pressure equipment.

Magnesium oxide (MgO) is one of the products of the pyrolysis and is typically obtained in powder form. The magnesium oxide is hydrated, eg, by quenching the MgO with water, thereby forming a magnesium hydroxide (Mg (OH) ₂ ) suspension. The magnesium hydroxide suspension is preferably recycled for use in the fermentation process. For example, the Mg (OH) ₂ can be used as a neutralizing agent in the fermentation process. In this case, the Mg (OH) ₂ can be first washed with water to remove chloride ions, typically to a content of less than 1000 ppm. The presence of chloride ions is undesirable because they can cause corrosion problems when added to the fermentation vessel. Since Mg (OH) ₂ has low solubility in water, such washing steps typically will not result in a significant amount of Mg (OH) ₂ loss. Alternatively, the Mg (OH) ₂ is first converted to magnesium carbonate (MgCO ₃ ), which is then used as a neutralizing agent in the fermentation process. Also, a combination of these two steps may be applied, in which part of the Mg (OH) ₂ is washed and reused and the second part is converted to MgCO ₃ and then the process Reused in A portion of the MgO can even be used directly in the fermentation. The HCl obtained in the pyrolysis step may be dissolved in water, thereby forming an aqueous HCl solution. Preferably, the HCl obtained in the pyrolysis step is recycled by using it in the acidification step in the process of the invention, for example as HCl gas or aqueous HCl solution.

The magnesium carboxylate provided in the method of the present invention can be obtained in a fermentation process. In such fermentation processes, carbohydrate sources are typically fermented by microorganisms to form carboxylic acids. A magnesium base is then added as a neutralizing agent during fermentation to provide the magnesium salt of the carboxylic acid. Examples of suitable magnesium bases are magnesium hydroxide (Mg (OH) ₂ ), magnesium carbonate (MgCO ₃ ) and magnesium bicarbonate (Mg (HCO ₃ ) ₂ ). The advantage of using Mg (OH) ₂ as a base is that this compound can be provided by the method of the invention. The use of MgCO ₃ is also desirable and can be easily obtained by converting Mg (OH) ₂ obtained in the process of the invention. Furthermore, the use of MgCO ₃ or Mg (OH) ₂ is desirable, since hydroxides and carbonates are not expected to have a negative effect on the salting out effect of the process of the invention (neutralization). Any remaining carbonate can leave the solution as gaseous CO ₂ ).

In one embodiment, the fermentation process may include a purification step in which the magnesium carboxylate obtained during crystallization is crystallized from the fermentation broth, which is then dissolved in water and then aqueous. A solution may be formed, which typically has a higher carboxylate concentration than the fermentation broth. Such a purification step may have the advantage that higher yields can be obtained in the first precipitation step because of the higher concentration of the magnesium carboxylate.

However, as described above, the magnesium carboxylate preferably remains in dissolved form when the magnesium base is added as a neutralizing agent. This has the advantage that the magnesium carboxylate is pumpable and can be used directly in the acidification step. Furthermore, the acidification step is easy to control when the magnesium carboxylate is in dissolved form. In particular, the magnesium carboxylate present in the magnesium carboxylate solution or suspension obtained after addition of the magnesium base is at least 90% by weight, preferably at least 95% by weight, more preferably at least 99% by weight magnesium. Contains the carboxylate in dissolved form. A small amount of solids (at most 10% by weight) may still not cause the adverse effects described above.

The crystallization may include at least one thickening step, such as a water evaporation step, a cooling step, a seeding step, a separation step, a washing step, and a recrystallization step. Thickening can be performed as a separate step or together with crystallization (eg evaporative crystallization).

The invention is further illustrated by the following examples.

Magnesium dicarboxylate preparation

Magnesium hydroxide was added to the aqueous solution of dicarboxylic acid and heated to complete dissolution. Four different carboxylic acids were used: adipic acid, fumaric acid, itaconic acid, and 2,5-furandicarboxylic acid. The amount of each component is given in Table 1. The resulting dicarboxylate solution was meant to resemble the magnesium dicarboxylate solution obtained in the fermentation process. The magnesium dicarboxylate solution obtained in the fermentation process generally contains compounds other than magnesium dicarboxylate, such as relatively large amounts of impurities, but the magnesium dicarboxylate solution prepared for this example is It appeared to be sufficiently similar to the resulting magnesium dicarboxylate solution to provide evidence of the principle by which the present invention works.

Dicarboxylic acid precipitation

An amount of an aqueous solution of HCl was added to the magnesium dicarboxylate solution from Example 1 as shown in Table 2. The temperature of the mixture thus obtained is also given in Table 2. The mixture was cooled to 20 ° C. and a precipitate formed. Samples of the solution were taken for each 10 ± 1 ° C. during cooling. The composition of the sample and the total amount of precipitate formed was determined.

The sample was taken only from the solution (for sampling, the stirrer was stopped for a few seconds and after the crystals precipitated, the sample was taken from the upper layer). Magnesium and dicarboxylic acid in the solution were analyzed and expressed as g / g water. The amount of crystals produced was calculated as the difference between the initial dicarboxy mass and the dicarboxy mass remaining in solution.

The results are shown in Tables 3 to 6 for each of adipic acid, fumaric acid, itaconic acid and 2,5-furandicarboxylic acid.

These results correspond to a total recovery of> 97% for adipic acid,> 72% for fumaric acid,> 80% for itaconic acid, and> 96% for 2,5-furandicarboxylic acid.

This example shows that adipic acid, fumaric acid, itaconic acid and 2,5-furandicarboxylic acid can be efficiently obtained using the method of the present invention. During precipitation, most of the dicarboxylic acid precipitates while substantially all of the magnesium ions remain in solution. It is concluded that acidification with HCl and subsequent crystallization results in a very efficient separation of the dicarboxylic acid from the magnesium dicarboxylate solution.

Citric acid precipitation

In the first experiments with citric acid, citric acid 5 g, it was added to a saturated solution of MgCl _2.

In a second experiment with citric acid, 15 g citric acid were added to a saturated solution of MgCl _2.

In a third experiment with citric acid, 5 g of magnesium chloride was added to a saturated solution of citric acid.

In a fourth experiment with citric acid, 15 g of magnesium chloride was added to a saturated solution of citric acid.

In all four experiments, a precipitate was formed. The citric acid and Mg content of the precipitate was analyzed using HPLC. The results are shown in Table 7.

This experiment shows that citric acid can be precipitated from magnesium chloride solution.

Claims (24)

A method for recovering carboxylic acid, comprising:
The step of preparing magnesium carboxylate, wherein the carboxylic acid corresponding to the carboxylate is 2,5-furandicarboxylic acid, fumaric acid, adipic acid, itaconic acid, citric acid, glutaric acid, maleic acid, malonic acid, Selected from the group consisting of oxalic acid and fatty acids having more than 10 carbon atoms;
Acidifying the magnesium carboxylate with hydrogen chloride (HCl), thereby obtaining a solution comprising carboxylic acid and magnesium chloride (MgCl ₂ ) , wherein the HCl is a gas or an aqueous solution comprising at least 5 wt% HCl; Prepared as a solution ;
Optionally, a thickening step, wherein the solution comprising carboxylic acid and MgCl ₂ is thickened; and
Precipitating the carboxylic acid from the solution containing carboxylic acid and MgCl ₂ , thereby obtaining a carboxylic acid precipitate and an MgCl ₂ solution;
Including
Said method;
Subjecting the MgCl ₂ solution to a pyrolysis step at a temperature of at least 300 ° C., thereby decomposing the MgCl ₂ into magnesium oxide (MgO) and HCl;
Dissolving the HCl formed in the pyrolysis step in water, thereby obtaining an HCl solution; and contacting the MgO with water, thereby obtaining Mg (OH) ₂ .
A method further comprising: The method according to claim 1, wherein the pyrolysis is performed using a spray roaster. The process according to claim 1 or 2, wherein the pyrolysis is carried out at a pressure of 0.1 to 10 bar. The method of claim 3, wherein the pyrolysis is performed at atmospheric pressure. The method according to claim 1, wherein the pyrolysis is performed at a temperature of 300 to 450 ° C. Mg (OH) ₂ is converted to MgCO _3, The method according to any one of claims 1 to 5. Thermal decomposition, by spraying the MgCl ₂ solution is effected by contacting a flow of hot gas, the method according to any one of claims 1-6. 8. A process as claimed in any one of the preceding claims, wherein acidifying the magnesium carboxylate and precipitating the carboxylic acid thus formed is performed in one step. The MgCl ₂ solution or the concentrated MgCl ₂ solution is subjected to a second precipitation step to recover at least a portion of the carboxylic acid remaining in the MgCl ₂ solution obtained in the first precipitation step; The method according to claim 1. The method according to claim 9, wherein the second precipitation is performed by cooling and / or concentrating the MgCl ₂ solution. Said second precipitation, the temperature of at least 30 ° C. below the temperature of 25 ° C., is carried out by the MgCl ₂ solution is cooled and / or thickening method of claim 9. Prior of the second precipitation, additional MgCl ₂ is added to the MgCl ₂ solution, The method according to any one of claims 9-11. The method according to any one of claims 1 to 12, wherein the carboxylic acid is selected from the group consisting of adipic acid, itaconic acid, 2,5-furandicarboxylic acid, and fumaric acid. The method includes a thickening step, in which the solution containing the carboxylic acid and MgCl ₂ is equal to or at most 5 g / L below the saturation point of the carboxylic acid. The method according to claim 1, wherein the method is enriched to a concentration. The method includes a thickening step, in which the solution containing the carboxylic acid and MgCl ₂ is equal to or at most 10 g / L lower than the saturation point of the carboxylic acid. The method according to claim 1, wherein the method is enriched to a concentration. 16. A process according to any one of claims 1 to 15, wherein the magnesium carboxylate is acidified with an HCl solution. The method of claim 16, wherein the HCl solution comprises at least 5 wt% HCl. The method of claim 16, wherein the HCl solution comprises at least 10 wt% HCl. The method of claim 16, wherein the HCl solution comprises at least 20 wt% HCl. 20. A method according to any one of the preceding claims, wherein the magnesium carboxylate is provided in dissolved form as part of an aqueous solution obtained in a fermentation process or as part of an aqueous suspension. . The aqueous solution or suspension comprises at least 10% by weight magnesium carboxylate based on the total weight of the solution or suspension, and the solution comprising the carboxylic acid and MgCl ₂ comprises a carboxylic acid. based on the total weight of the solution containing MgCl ₂ of at least 5 wt%, the method of claim 20. The aqueous solution or suspension comprises at least 15% by weight magnesium carboxylate based on the total weight of the solution or suspension, and the solution comprising the carboxylic acid and MgCl ₂ comprises a carboxylic acid. based on the total weight of the solution containing MgCl ₂ of at least 10 wt%, the method of claim 21. The magnesium carboxylate is obtained in a fermentation process, the process comprising a purification step, wherein the magnesium carboxylate is crystallized from the fermentation broth and then optionally dissolved in water to form an aqueous solution; 23. A method according to any one of claims 1-22. The magnesium carboxylate is obtained in a dissolved form in a fermentation process, the process comprising a purification step, wherein the carboxylic acid is neutralized by adding a magnesium base, during which the magnesium carboxylate is 23. A method according to any one of the preceding claims, which remains in dissolved form.